The present invention relates to a device for a curved conductor pipe for a pull wire.
In a known conductor pipe of this kind, the material yield point of the conductor pipe is equal to or less than the compressive force which operates between the pull wire and the conductor pipe.
When oil production platforms are set up, large gas/oil pipes are pulled into couplers at the bottom of the platforms. To pull these pipes, a pull wire is used which is fed through a conductor pipe that is connected in a watertight manner to the gas/oil pipe coupler. The conductor pipe continues upwards into the platform shaft to a level above the surface of the water. The conductor pipe would normally always be made with a curve in the range of 80.degree.-90.degree. immediately after the connection to the gas/oil pipe coupler. This means that the conductor pipe is subjected to great stress, especially in instances when large gas/oil pipes are pulled into place, where the traction forces in question may be as much as 300-500 tonnes.
Normally the conductor pipe is made of a weldable steel of the St52-3 type or similar. This quality is chosen inter alia for the following reasons:
Good extension properties which provide ample protection against local peak loads and cracking. PA1 Good welding properties which provide a secure welded connection of flanges and fixing equipment. PA1 The pipe quality is a standard commodity and lends itself to induction bending of curves.
However, the recited steel quality has a major disadvantage for precisely the purpose as outlined above for which the steel is used in conductor pipes for pulling oil/gas pipes in connection with oil/gas installations. The pipe has a Brinell hardness in the range of 180-200. A further disadvantage is that a pull wire will not have a sufficently good seat when it is pulled through a curved conductor pipe of this kind. This is due to the contact face against the bend of the pipe being extremely small, virtually tangential, which in turn results in the compressive force between the wire and the curved conductor pipe rapidly exceeding the yield point of the conductor pipe (approx. 3,500 kg/cm.sup.2).
These last-mentioned factors will in turn result in the rasping away of steel material in the conductor pipe where the wire slides, and consequently a greatly increasing friction quotient between the conductor pipe and the pull wire. In turn, this leads to reduced net hoisting power, since a great part of the winch power which is used to pull in the wire is used not least to overcome the friction between the conductor pipe and the pull wire. This results in increased wear and tear on the conductor pipe, which in turn could result in breaks in the conductor pipe and, in its most unfortunate consequence, could result in the platform leg filling up with sea water.